1. Field of the Invention
The present invention relates to a power transfer device adapted for use in combination with a power transmission for a four-wheel drive vehicle to selectively provide either a high speed two-wheel drive, a high speed four-wheel drive or a low speed four-wheel drive.
2. Description of the Prior Art
In Japanese Patent Publication No. 57-54333, there has been proposed a shift mechanism in a power transfer device of this kind, which shift mechanism includes first and second shift rods axially slidably mounted in parallel to each other within a housing of the transfer device, an interlock mechanism arranged to selectively retain the shift rods in their shifted positions, an operation rod in the form of a cross-rod arranged perpendicularly to the shift rods and rotatably supported on the peripheral wall of the housing to be rotated by means of a manually operated transfer lever, an inner shift lever fixedly mounted on the operation rod for rotation therewith, and a swing lever pivoted to the inner shift lever and having one end portion engaged with the first shift rod and the other end portion engaged with the second shift rod. When the operation rod is rotated in one direction, the one end portion of the swing lever is retained as a fulcrum so that the other end portion of the swing lever swings to move the second shift rod from a four-wheel drive position to a two-wheel drive position. When the operation rod is rotated in another direction, the other end portion of the swing lever is retained as a fulcrum so that the one end portion of the swing lever swings to move the first shift rod from a high speed position to a low speed position.
In such a conventional shift mechanism as described above, the distance between the pivot axis of the swing lever and the one end portion of the same in engagement with the first shift rod is substantially the same as the distance between the pivot axis of the swing lever and the other end portion of the same in engagement with the second shift rod. With such arrangement of the swing lever, the axial movement amount of the second shift rod caused by rotation of the operation rod is substantially the same as that of the first shift rod caused by rotation of the operation rod. As a result, the shift amount of the transfer lever for effecting the axial movement of the second shift rod is substantially the same as that of the transfer lever for effecting the axial movement of the first shift rod. In practical use of the transfer device, however, the second shift rod is frequently shifted in comparison with the first shift rod to selectively establish a two-wheel drive power train or a four-wheel drive power train. It is, therefore, desirable that the shift distance of the transfer lever for effecting the axial movement of the second shift rod is reduced to less than that of the transfer lever for effecting the axial movement of the first shift rod, to enhance maneuverability of the transfer device.